Reliability of operation is an important consideration for modern electronic devices, e.g., selective call receivers. One aspect of reliability is the device's ability to continue to function properly after sudden mechanical impacts and shocks, e.g., dropping the unit onto a hard surface. Modern selective call receivers, e.g., pagers, generally include relatively thin printed circuit boards, housings which are typically made of a plastic type material, and fragile electronic components. The plastic housing's front and back planes and internal printed circuit boards mounted within the housing typically have a low mechanical frequency response to sudden impacts, resulting in relatively large deflections. The deflecting front and back planes, as well as the deflecting printed circuit boards, can impact with each other, resulting in primary and secondary impacts with the components supported by the printed circuit boards. Certain ones of these components are fragile in nature, e.g., constructed of quartz, ceramic, and silicon, making them especially susceptible to failure due to mechanical shocks. Additionally, each of these components also has a natural mechanical frequency response to impact that can amplify the incoming shock and cause serious damage to the component.
Furthermore, modern low volumetric selective call receivers do not permit height tolerances between the printed circuit boards and the housing front and back surfaces to accommodate large deflections. As a result, sudden mechanical shocks typically cause primary and secondary impacts between the deflecting structures. Moreover, any large mass objects such as a battery, contained within the housing of the electronic device, will tend to resist motion due to their inertia, frequently causing secondary shocks and often catastrophic mechanical failure in areas proximate to their location. All of these effects can result in unit failures.
As an example, large impacts, whether primary or secondary, can create detached or broken solder joints in integrated circuits, ceramic filters, and other components. Further, excessive printed circuit board deflections can overstress and fatigue solder joints resulting in failure.
The current method of providing shock isolation within a selective call receiver is to place one or more pieces of shock isolating material in selected areas, usually along stiffeners (e.g., such as ribs in an airplane wing, portions that are added for rigidity that tend to resonate) or the like. Unfortunately, this approach provides a limited amount of shock isolation in a single direction only, and does not solve all of the problems described above. Further, if during manufacturing of the selective call receiver, the shock isolating material is not correctly placed or missing, the final delivered product is again susceptible to failures due to mechanical shock as discussed above.
Thus, what is needed is an apparatus for isolating shock sensitive portions of the electronic device from primary and secondary mechanical shock, thus reducing the resulting deflections of the device's constituent parts and improving reliability over the device's operating lifetime.